1. Field of the Invention
The present invention relates to a liquid crystal display apparatus excellent in light utilizing efficiency, bright and easy to see a display.
2. Description of the Related Art
Such a liquid crystal display apparatus for both of reflection and transmission has been investigated which is added with an illumination device to be visually recognized as a transmission type liquid crystal display apparatus at dark places, as making the most of merits of a reflection type liquid crystal display apparatus less to consume electricity. There has been proposed an apparatus equipped with a semi transmission type reflecting plate between a back light and a liquid crystal cell in the transmission type liquid crystal display apparatus. However a system making use of the semi transmission type reflecting plate has brought a problem that since a light is divided into a reflected light and a transparent light owing to a half mirror effect, a brightness does not come up to a brightness exclusive for reflection or transmission in either mode of reflection and transmission.
In view of the above mentioned states, an improvement has been also proposed using a reflection type polarizer where polarization is selectively reflected and a total of reflectance and transmissivity can be beyond 100%. But, a problem is that owing to difference in polarization characteristic (a polarizing plane of linear polarization is 90xc2x0 different) in the reflected light and the transparent light, displays by the reflection mode and the transmission mode are inverted, and as the reflection mode is dark under twilight, if turning to the transmission mode, a contrast is made unstable by inversion of the display, and displays in either mode are not easy to see.
On the other hand, another problem is that if brightening in the transmission mode, blackness of a black display lacks to lower the contrast, and if a light absorbing substance is arranged for preventing the black display from insincerity, the display becomes dark by the light absorption thereby.
The invention has a theme to develop such a liquid crystal display apparatus of good visibility being excellent in bright-ness under both modes of reflection and transmission, not causing inversion of the display, and excellent in contrast even under twilight or the like.
The invention is to offer a liquid crystal display apparatus, characterized by providing a reflection type polarizer which emits an incident light coming from a light source disposed on an incident side face from a lower surface via a light emitting means formed on an upper surface, divides an incident natural light into a reflected light and a transparent light at the lower surface side, and supplies the reflected light made of a circularly polarized light, and disposing a liquid crystal shutter having a liquid crystal cell and at least one sheet of polarizer on the upper surface side of a light pipe passing the reflected light from the upper surface.
According to the invention, since the liquid crystal display is accomplished through an external light by the reflection type polarizer of the lower surface of the light pipe or reflected light of an emitting light from the light pipe, it is possible to provide such a liquid crystal display apparatus of good visibility being excellent in brightness under both modes of reflection and transmission, not causing inversion of display, and excellent in contrast even under twilight or the like, in which the display is not inverted owing to differences of polarization characteristic in both modes of reflection and transmission, and the contrast is not influenced by leakage light from the light pipe.
Further, by supplying the reflected light comprising the circularly polarized light, the display having the excellent contrast in both modes of reflection and transmission can be accomplished even in a system of arranging a single layer of the polarizer omitting a visually rear side, and brightness can be also improved by reduction of absorption loss by omitting the visual rear side. Accordingly it is possible to accomplish the display by far heightening the contrast than an existing reflection type liquid crystal display apparatus of the system of arranging a single layer of the polarizer including a matter to become a circularly polarized light after the external light passes through the cell, and it is possible to add a displaying function by the transmission mode.
As light emitting means is installed on the upper surface, an optical path within the light pipe can be lengthened in the transmission mode, so that light can be largely expanded to enable to moderate strength of bright line and advantageously serve to prevent moire and improve uniformity of brightness, and the reflection type polarizer can be closely and easily attached as one body to the lower surface of the light pipe via an adhesive layer. In case the light emitting means is provided to the lower surface of the light pipe, the reflection type polarizer should be separately located from the viewpoint of maintaining the function of the light emitting means, and a structure is complicated by locating and fixing it together with increase of the number of parts, and wrinkles appear to demand a thick support for avoiding disturbance of display so that a difficulty occurs of heavy weight.
In the case of the light pipe having the light emitting means comprising obliquity of prismatic structures, the inventive liquid crystal display apparatus is excellent in directivity of reflected light coming through the obliquity, and can effectively form light useful to visibility in the transmission mode and realize a brighter display, and this is excellent in injection efficiency of an external light and transmission efficiency after reflection, so that even in the reflection mode it is possible to provide a brighter display by emission surpassing uniformity. The moire occurrence owing to directivity can be restrained by the oblique arrangement of the light emitting means, thereby enabling to avoid glittering obstacle of visual recognition.
In the light pipe having the above mentioned scattering type emitting means of dotting- or crimping-like structures, light is emitted at a large angle of about 60 degrees, so that a front (vertical) direction becomes a dark transmission mode difficult to see. If a prism sheet is laid aiming at controlling the optical path, light in the reflection mode is scattered and is scarcely contributed to the visual recognition and makes a very dark display. In addition, if dots are clearly seen and a diffusing layer having a strong diffusion is disposed for avoiding dot scattering, the reflected light by the incident light in the reflection mode and the reflecting layer thereof is also scattered to turn out a dark display.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.